Abstract:
The kinetics and mechanism of phase transitions (PTs) in gibbsite (γ-Al(OH)3) under heat treatment in air and water vapor (170-550°C) have been investigated by iso-and nonisothermal thermogravimetry, X-ray phase analysis, transmission electron microscopy, 27Al nuclear magnetic resonance, and chemical analysis. It is shown that (i) the gibbsite PT in air involves two interrelated transformations occurring simultaneously: (1) gibbsite → boehmite (γ-AlOOH) and (2) gibbsite → X-ray-amorphous alumina (Al2O3); both are implemented through the topochemical mechanism; and (ii) in water vapor only transformation of gibbsite into boehmite occurs (PT-3), which is implemented through the dissolution-precipitation mechanism. The apparent activation energies of the PTs under consideration have been determined. © Allerton Press, Inc. 2007.